Optical location systems are increasingly being used to locate mobile items in a defined area. An example of an application is locating light emitting product items during their movement from one workstation to another in a manufacturing plant.
Typical optical location systems involve at least one object, i.e., target, that moves within an area whose perimeter is defined by the range of the transmitters and receivers. In some systems, the target carries the transmitter and the receiver is stationary; in others, the target receives a transmitted signal. In a third type of system, the target reflects transmitted radio or light waves back to a receiver.
An advantage of placing the transmitting device on the target is that the transmitted signal may then contain data identifying the target. Optical location systems using a transmitter attached to the target are described in U.S. Pat. No. 4,710,028 to Grenier, et al, and in U.S. Pat. No. 3,614,240 to Brandts, et al. These systems use a matrix of photosensitive elements, and the coordinate position of a sensitized element is used to determine the position of the target.
Typically, the signals used in optical location systems are infrared and suffer from high background noise due to ambient light, such as daylight, incandescent, and fluorescent light. Because of this, many systems are required to operate in dark or low light conditions. However, this is impractical for many applications, such as tracking locations of items in a manufacturing plant.
A need exists for an optical location system that has decreased sensitivity to noise resulting from ambient light. However, such a system should not be prohibitively expensive in terms of its optical and electro-optical devices.